US3816828A - Echo protection for tacan/dme - Google Patents

Echo protection for tacan/dme Download PDF

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Publication number
US3816828A
US3816828A US00253715A US25371572A US3816828A US 3816828 A US3816828 A US 3816828A US 00253715 A US00253715 A US 00253715A US 25371572 A US25371572 A US 25371572A US 3816828 A US3816828 A US 3816828A
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Prior art keywords
dead time
coupled
gate
receiver
output
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Expired - Lifetime
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US00253715A
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English (en)
Inventor
M Jezo
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TDK Micronas GmbH
ITT Inc
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Deutsche ITT Industries GmbH
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Priority to US00253715A priority Critical patent/US3816828A/en
Priority to DE2323979A priority patent/DE2323979A1/de
Priority to FR7317722A priority patent/FR2184921A1/fr
Application granted granted Critical
Publication of US3816828A publication Critical patent/US3816828A/en
Assigned to ITT CORPORATION reassignment ITT CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: INTERNATIONAL TELEPHONE AND TELEGRAPH CORPORATION
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
    • G01S13/76—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted
    • G01S13/762—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted with special measures concerning the radiation pattern, e.g. S.L.S.

Definitions

  • ABSTRACT 52 11.5. c1. 343/65 13c This invention relates to a method and apparatus for 51 int. c1.. G015 9/56 inhibiting the receiver of a Tactical Air Navigation 53 Field f Search 343 5 5 LC 3 R, (TACAN) system from responding to invalid interro- 343 g LC gations (echoes).
  • First and second dead time gates are generated.
  • the second dead time gate has a fixed du- 5 References Cited ration and is jittered within a predetermined time UNITED STATES PATENTS range.
  • Each dead time gate is used to inhibit the beacon receiver from responding to an invalid interroga- 3,349,402 10/1967 Foster 343/65 R tion 3,643,256 2/1972 Owen 1.
  • This invention relates to a method and apparatus for inhibiting the receiver of a Tactical Air Navigation (TACAN) system from responding to invalid interrogations.
  • TACAN Tactical Air Navigation
  • a TACAN system of the type described in MIL-STD 291B receives interrogation signals from airborne transponders. However, the receiver is interested only in the interrogation signals which propagate along the direct path from the aircraft to the ground beacon, and not in echoes or reflections of the interrogation which arrive at the ground beacon via multipath propagation, i.e., reflected off the surface of the earth or buildings, vehicles, etc. to the ground beacon.
  • SUMMARY OF THE INVENTION .It is an object of the present invention to provide a method and apparatus for minimizing the effects of airto-ground multipath signals.
  • the echo suppression system proposed provides controls that permit the sensitivity time characteristics of the receiver, following the reception ofa pulse, to be tailored to the echo characteristics of the beacon site.
  • a method of inhibitingthe receiver of a Tactical Air Navigation system from responding to invalid interrogations comprising receiving signals in a receiver, decoding said signals which represent interrogations, generating a first dead time gate having a predetermined duration, said first dead time gate beginning immediately after the decoding of an interrogareceiver of a Tactical Air Navigation system from responding to invalid interrogations comprising a receiver for decoding interrogations, first means coupled to said receiver for generating a first dead time gate, second means coupled to said first means for generating a second dead time gate and means coupled to said first means and said secondmeans for combining said first dead time and said second dead time, said combining means coupled to said receiver for inhibiting any further decoding of interrogations during the time duration of either said first or second dead time gate.
  • FIG. 1 shows an example of countdown as a function of delay for a dead time gate having a trailing edge jitter between and 200 microseconds;
  • FIG. 2a illustrates the timing relationship between decoding of an interrogation and the first and second dead time gates according to the present invention
  • FIG. 2b shows the countdown as a function of delay when using a trailing edge second gate which is 35 microseconds wide and is jittered between 25 microseconds and microseconds;
  • FIG. 3 shows countdown as a function of delay in which the echo rejection is set for an echo having delays between 130 and 200 microseconds;
  • FIG. 4 is a functional block diagram of a circuit which provides first and second dead time gates according to the invention.
  • FIG. 5 is a timing diagram illustrating the generation of first and second dead time gates by the circuit shown in FIG. 4.
  • Echoes of interrogations can be divided into two categories. The first are specular reflections which arise from large areas. The receiver output, due to specular reflection, resembles decaying noisy CW. In severe cases, echoes can remain above the noise level for several hundred microseconds.
  • Lengthening the dead time gate is a poor solution for this problem as the standard pulse distribution can no longer be maintained in heavy traffic conditions, and countdown becomes excessive. It creates excessive dead time, even for an interrogation just above the noise, which has no detectable echo.
  • the time characteristics of the receiver, followingthe reception of a pulse can be tailored to the echo characteristics of the beacon site according to this invention. This permits receiver blanking, following the reception of a pulse, without receiving the specular reflection dueto the pulse.
  • the second category of echoes are point reflections from a single area which is normally relatively small.
  • the resulting echo is a decent delayed replica of the interrogation.
  • Such reflections have been observed to last for a long time after the real interrogation with amplitudes within a few db of the true interrogation. Further protection in these cases can be attained by jittering the trailing edge of the dead time. littering makes the spurious replies to the aircraft non-synchronous, thus greatly reducing the possibility of an airborne lock-on spurious reply.
  • a disadvantage of this method is that the average dead time is somewhat greater than it would be without jitter because the minimum dead time must be the same in both cases.
  • FIG. 1 Since efficient protection against echoes is obtained with 50 percent countdown, one can see from FIG. 1 that there is over protection near 60 microseconds and under protection near 200 microseconds delay.
  • the curve shown as FIG. 1 corresponds to a fixed dead time gate of 130 microseconds having a 50 percent countdown capability.
  • the invention proposes the use of two dead time gates to improve the above-described situation.
  • first gate is the regular dead time gate following the interrogation decode shown in FIG. 2a. This gate normally provides for 60 microseconds dead time.
  • the second gate is of a fixed duration and its position is jitteredbetween two predetermined limits suitable for the particular echo situation of the beacon site.
  • FIG. 2b shows the countdown as a function of delay when using a trailing edge second gate, shown in FIG. 2a, which is 35 microseconds wide and is jittered between 25 and I30 microseconds.
  • the echo protection is the same as in the previous example since the countdown of the echoes is 50 percent but the countdown for real interrogation corresponds to a fixed dead time gate of 103.75 microseconds.
  • FIG. 3 shows that this technique allows for tailoring the echo rejection to each site.
  • the echo rejection is set for an echo having delays between I30 and 200 microseconds.
  • receiver decode unit 4 interrogations and echoes are applied to receiver decode unit 4 on terminal 1.
  • the decoded output of receiver decode unit 4 is shown on line 1 of FIG. 6.
  • This output triggers one shot 10, shown on line 2 of FIG. 5, and corresponds to the first transformer dead time gate.
  • the trailing edge of the signal generated by one shot sets flip-flop 15.
  • Flip-flop remains set until reset by the rising edge of free running astable multivibrator 3.
  • there is no coherence bej 4 tween the astable multivibrator 3 and one shot 10 successive set times of flip-flip 15 very randomly. Distribution of the set times is linear, with limits of 0 to the period P, of astable multivibrator 3.
  • the jitter can be disabled by disconnecting the input terminal 14 of OR gate 5 by means of dead time jitter switch 1 1.
  • An apparatus for inhibiting the receiver of a Tactical Air Navigation system from responding to invalid interrogations comprising:
  • first means coupled to said receiver for generating a first dead time gate
  • second means coupled to said first means for generating a second dead time gate
  • said means for varying including a flip-flop having set and reset input terminals, said set terminal coupled to the output of said first means, and having an output coupled to the input of said second means;
  • an astable multivibrator having an output coupled to said reset terminal.
  • said combining means is an OR gate having its first input coupled to the output of said first means and its second input coupled to the output of said second means.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar Systems Or Details Thereof (AREA)
US00253715A 1972-05-16 1972-05-16 Echo protection for tacan/dme Expired - Lifetime US3816828A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US00253715A US3816828A (en) 1972-05-16 1972-05-16 Echo protection for tacan/dme
DE2323979A DE2323979A1 (de) 1972-05-16 1973-05-11 Unterdrueckung von reflektierten signalen bei tacan-systemen
FR7317722A FR2184921A1 (cs) 1972-05-16 1973-05-16

Applications Claiming Priority (1)

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US00253715A US3816828A (en) 1972-05-16 1972-05-16 Echo protection for tacan/dme

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US00253715A Expired - Lifetime US3816828A (en) 1972-05-16 1972-05-16 Echo protection for tacan/dme

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DE (1) DE2323979A1 (cs)
FR (1) FR2184921A1 (cs)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5248491A (en) * 1975-10-16 1977-04-18 Nec Corp Receiver for range finding signal of pair pulse type characterized by suppressing function for interference reflecting wave

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3349402A (en) * 1960-11-03 1967-10-24 Cossor Ltd A C Secondary radar systems
US3643256A (en) * 1969-03-04 1972-02-15 Cossor Ltd A C Secondary radar system
US3646556A (en) * 1970-03-25 1972-02-29 Us Navy Reflected iff interrogation rejector
US3680090A (en) * 1970-07-27 1972-07-25 Us Navy Non-main beam reflected iff interrogation rejector
US3715750A (en) * 1970-07-31 1973-02-06 Us Navy Omnidirectional reflected interrogation rejector

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3349402A (en) * 1960-11-03 1967-10-24 Cossor Ltd A C Secondary radar systems
US3643256A (en) * 1969-03-04 1972-02-15 Cossor Ltd A C Secondary radar system
US3646556A (en) * 1970-03-25 1972-02-29 Us Navy Reflected iff interrogation rejector
US3680090A (en) * 1970-07-27 1972-07-25 Us Navy Non-main beam reflected iff interrogation rejector
US3715750A (en) * 1970-07-31 1973-02-06 Us Navy Omnidirectional reflected interrogation rejector

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5248491A (en) * 1975-10-16 1977-04-18 Nec Corp Receiver for range finding signal of pair pulse type characterized by suppressing function for interference reflecting wave

Also Published As

Publication number Publication date
DE2323979A1 (de) 1973-12-06
FR2184921A1 (cs) 1973-12-28

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Free format text: CHANGE OF NAME;ASSIGNOR:INTERNATIONAL TELEPHONE AND TELEGRAPH CORPORATION;REEL/FRAME:004389/0606

Effective date: 19831122